Desmoplastic trichilemmoma of the scalp: case report and literature review of immunohistochemical staining features.

Desmoplastic trichilemmoma (DT) of the scalp is a rare disease. In this report, we describe a 67-year-old man who had a small papule lesion around the hairline of the left scalp for more than 40 years. The lesion had rapidly grown to become a solitary, round, 15-mm neoplasm within 6 months. Histopathological examination showed that the mass was composed of a peripheral layer of columnar cells with nuclear palisading resembling the outer root sheath; the mass was surrounded by a thickened glassy basement membrane. The stroma in the center of the mass displayed solid, hyaline degeneration and an eosinophilic pattern, streaked with epithelial cords or islands. Immunohistochemical evaluation showed diastase-resistant, periodic acid–Schiff-positive desmoplastic stroma at the center, and Ber-EP4-negative tumor cells (CD34-positive focally and Bcl-2-positive at the periphery). The tumor was completely resected, and no recurrence occurred during the follow-up period. In this report, we also summarize immunohistochemical features from previous reports of DT, facilitating differential diagnosis of DT from some invasive skin tumors.